text: The coordination of alkynes to transition metals is similar to that of alkenes. The bonding is described by the Dewar–Chatt–Duncanson model. Upon complexation the C-C bond elongates and the alkynyl carbon bends away from 180º. For example, in the phenylpropyne complex Pt(PPh)(MeCPh), the C-C distance is 1.277(25) vs 1.20 Å for a typical alkyne.  The C-C-C angle distorts 40° from linearity upon complexation.  Because the bending induced by complexation, strained alkynes such as cycloheptyne and cyclooctyne are stabilized by complexation.
  The C≡C vibration of alkynes occurs near 2300 cm in the IR spectrum.  This mode shifts upon complexation to around 1800 cm, indicating a weakening of the C-C bond.